Laser systems may incorporate collections of two or more laser diodes either as the direct source of the output laser radiation, or as a pump for a diode-pumped laser such as a fiber laser, a disk laser, a slab laser, a rod laser, a diode-pumped solid-state laser, a Raman laser, a Brillouin laser, an optical parametric laser, or an alkali-vapor laser.
Many laser applications require tunable laser output power from near zero power up to maximum power. In materials-processing applications, for example, low power levels may be required for alignment or pre- or post-treatment steps, whereas high power levels may be used for the actual processing steps such as cutting, welding, drilling, or scribing. As a second example, in a flexible machine intended for laser processing of a wide range of material types or thicknesses, certain applications may demand significantly lower power than others. To date, most lasers that are used in such applications provide such power tuning by varying the current applied to the laser diodes between zero and the current required for maximum power, equal currents being applied to each diode.
However, the laser diodes that generate the laser power may operate best within a high power range, therefore it may be preferable to operate the laser diodes within the high power range. In such situations it may not be possible or desirable to operate the laser diodes at individual powers spanning from low power to maximum power.
In a known power tuning method, the laser system is operated at constant, full power and a variable attenuator or modulator downstream is used to attenuate the output of the laser system. However, such attenuators or modulators may not be available or reliable at the power levels or operating wavelengths of interest, and, if available, may add significant cost to the system. Additionally, attenuation or modulation of full power to lower power levels achieved in this manner wastes energy.
Accordingly, there is a need for a low-cost, reliable technique to provide broad power tuning in an energy efficient manner.